Method and apparatus for examining a measuring tip of a scanning probe microscope

ABSTRACT

The present invention relates to a method for examining a measuring tip of a scanning probe microscope, wherein the method includes the following steps: (a) generating at least one test structure before a sample is analyzed, or after said sample has been analyzed, by the measuring tip; and (b) examining the measuring tip with the aid of the at least one generated test structure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority under 35U.S.C. § 120 from PCT Application No. PCT/EP2018/067835, filed on Jul.2, 2018, which claims priority from German Application No. 10 2017 211957.8, filed on Jul. 12, 2017. The entire contents of each of thesepriority applications are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a method and an apparatus for examininga measuring tip of a scanning probe microscope.

BACKGROUND

Scanning probe microscopes use a measuring tip to sense a sample or thesurface thereof and thus yield measurement data for producing arepresentation of the topography of the sample surface. Below, scanningprobe microscopes are abbreviated SPM. A distinction is made betweenvarious SPM types depending on the type of interaction between themeasuring tip and the sample surface. Use is often made of scanningtunneling microscopes (STM), in which a voltage is applied between thesample and the measuring tip, which do not touch one another, and theresulting tunneling current is measured.

In the microscope referred to as atomic force microscope (AFM) orscanning force microscope (SFM), a measuring probe is deflected byatomic forces of the sample surface, typically attractive van der Waalsforces and/or repulsive forces of the exchange interaction.

In addition to these conventional SPM types, there are a multiplicity offurther appliance types which are used for specific fields ofapplication, such as e.g. magnetic force microscopes or optical andacoustic near-field scanning microscopes.

The disturbance in an image recorded by scanning a probe of an SPM thatis caused on account of a non-ideal geometry of a measuring tip is asignificant restriction of the nanometric measurement technique of ascanning probe microscope. This particularly applies to samples with alarge aspect ratio, in particular if the aspect ratio of the samplesurface comes close to the geometry of the measuring tip or even exceedsthe latter. In order to check whether this is the case, use is made oftest bodies with test structures for analyzing the geometry or the formof a measuring tip of a probe of a scanning probe microscope. Thefollowing documents describe the production of a test structure forascertaining the geometry or the form of a measuring tip of the probe ofa scanning probe microscope: U.S. Pat. No. 5,960,255, DE 101 07 796 A1,EP 0 676 614 A1 and U.S. Pat. No. 8,650,661 B2.

The following documents consider how to take account of the influence ofthe geometry or form of a measuring tip of an SPM on SPM images of asample surface: V. Bykov et al.: “Test structure for SPM tip shapedeconvolution,” Appl. Phys. A 66, p. 499-502 (1998); G. Reiss et al.:“Scanning tunneling microscopy on rough surfaces: Deconvolution ofconstant current images,” Appl. Phys. Lett. 57 (9), Aug. 27, 1990, p.867-869; Y. Martin and H. K. Wickramasinghe: “Method of imagingsidewalls by atomic force microscopy,” Appl. Phys. Lett. 64 (19), May 9,1984, p. 2498-2500; L. Martinez et al.: “Aspect-ratio andlateral-resolution enhancement in force microscopy by attachingnanoclusters generated by an ion cluster source at the end of a silicontip,” Rev. Sci. Instrum. 82, (2011), p. 023710-1-023710-7; X. Qian etal.: “Image simulation and surface reconstruction of undercut featuresin atomic force microscopy,” SPIE Proc. Vol. 6518, (2007), p. 1-12; L.Udpa et al.: “Deconvolution of atomic force microscopy data for cellularand molecular imaging,” IEEE, Sig. Proc. Mag. 23, 73 (2006); Ch. Wong etal.: “Tip dilation and AFM capabilities in the characterization ofnanoparticles,” J. O. Min. 59, 12 (2007); J. S. Villarrubia: “Algorithmsfor scanned particle microscope image simulation, surfacereconstruction, and tip estimation,” J. Res. Natl. Inst. Stand. Technol.102, p. 425-454 (1997); X. Qian and J. S. Villarrubia: “Generalthree-dimensional image simulation and surface reconstruction inscanning probe microscopy using a dexel representation,” Ultramicroscopy1008 (2007), p. 29-42.

Scanning probe microscopes can be used in different operating modes.

In all modes of operation, the measuring tips of scanning probemicroscopes are subject to wear as a result of the interaction with thesample. The degree of wear or abrasion depends, inter alia, on the modeof operation of the SPM and the type of interaction between themeasuring probe and the sample. The following publications consider thewear of a measuring tip of a probe of an SPM: J. Schneir et al.:“Increasing the value of atomic force microscopy process metrology usinghigh-accuracy scanner, tip characterization, and morphological imageanalysis,” J. Vac. Sci. Technol. B14(2), March/April 1996, p. 1540-1546;G. Dahlen et al.: “Tip characterization and surface reconstruction ofcomplex structures with critical dimension atomic force microscopy,” J.Vac. Technol. B 23(6), November/December 2005, p. 2297-2303; G. Dahlenet al.: “Critical dimension AFM tip characterization and imagereconstruction applied to the 45 nm node,” SPIE Proc. Vol. 6152, p.61522R-1 to 61522 R-11; J. E. Griffith and D. A. Grigg: “Dimensionalmetrology with scanning probe microscopes,” J. Appl. Phys. 74 (9), 1Nov. 1993, p. R83-R109.

In addition to wear, measuring tips may also become dirty during theiroperation. Both wear and dirtying of the measuring tip of a scanningprobe microscope have an influence on the quality of the measurementdata, and hence on the quality of the image of the surface of a samplegenerated therefrom.

One option for at least partly escaping the above-described problemconsists of a regular replacement of a probe of a scanning probemicroscope, without a preceding check of the state of the measuring tipof the probe. This procedure firstly leads to rejection of probes thatare still usable, which is connected to significant costs, and secondlyresults in long downtimes of the scanning probe microscope on account ofthe frequent changing of the probes.

The present invention therefore addresses the problem of specifying amethod and an apparatus that allow an optimization of the use of ameasuring tip of a scanning probe microscope.

SUMMARY

According to one exemplary embodiment of the present invention, thisproblem is solved by a method for examining a measuring tip of ascanning probe microscope. The method includes the following steps: (a)generating at least one test structure before a sample is analyzed, orafter said sample has been analyzed, by the measuring tip; and (b)examining the measuring tip with the aid of the at least one generatedtest structure.

Should the measuring tip of a scanning probe microscope not be replacedin preventative fashion at regular intervals, it is necessary—asdescribed in the preceding section—to determine the geometry or the formof the measuring tip from time to time in order to determine the wearand/or the degree of dirtying of a measuring tip of an SPM. Typically,this requires the sample to be examined to be replaced by a test body.Alternatively, the probe can be disassembled from the SPM in order toanalyze the measuring tip of the said probe externally with the aid of atest body that carries a test structure. Both are very time-consumingprocesses, particularly if the scanning probe microscope is operated ina vacuum environment.

A method according to the invention avoids these time-consumingprocesses by virtue of a test structure being generated in situ withinthe scope of an analysis process for a sample where necessary, saidanalysis process being carried out with the aid of a measuring tip of anSPM and said test structure being used to examine the current geometryor form of the measuring tip. This can reduce the downtime of an SPM, ora throughput of samples to be examined by a scanning probe microscopecan be increased.

Further, a test structure on an external test body is subject to wearand/or dirtying. Therefore, the topography of the test structure must beanalyzed at periodic intervals and cleaned where necessary. This leadsto a further time-consuming cleaning process, which significantlyimpedes the workflow in many analysis processes of samples carried outby a measuring tip of a scanning probe microscope.

A method according to the invention defines the in situ production of atest structure in the surroundings or vicinity of its use location.During the directly subsequent examination of the measuring tip usingthe generated test structure, the latter has neither been worn down norsubject to dirtying.

SPMs are frequently used to detect the contour of defects of a sample.Should this detection not yield a realistic image of the contour of adefect or of one or more marks that are used for aligning a repairapparatus in respect of a defect on account of a form of the measuringtip used for scanning purposes that is not exactly known, a correctionof the defect may fail and, in the worst case, even exacerbate thedefect.

A test structure generated once is available for a regular examinationof the measuring tip of the SPM and thereby reduces the risk of anerror-afflicted analysis of the contour of a defect and/or of the repairor compensation thereof.

The expression “after a sample has been analyzed by the measuring tip”includes the scanning of the sample being interrupted should signs thatthe measuring tip of the SPM is not suitable or only has qualifiedsuitability for sensing the sample arise during the simultaneouslycarried out analysis of the measurement data generated by use of thescanning. Further, the aforementioned passage does not preclude thegeneration of a test structure and the analysis of a sample by themeasuring tip being carried out at the same time.

The at least one test structure can be generated on the sample and/or ona substrate. The substrate can be disposed in a vacuum chamber in whichthe sample is analyzed and is disposed at a site in the vacuum chamberof the scanning probe microscope that is accessible to the measuringtip. The substrate may comprise a sample stage and/or a sample holder.

The generation of the at least one test structure may comprise adeposition of at least one test structure and/or an etching of the atleast one test structure.

The most important part of a test structure is the contour thereof.Whether this contour is generated by depositing material on a substrate,by etching the test structure into a substrate and/or by depositingmaterial on a substrate and subsequently etching the test structure intothe deposited material is unimportant for the functioning thereof.

A contour of the at least one test structure may be matched to a contourof the sample.

An advantage of generating a test structure in situ is that the contourthereof can be matched to the contour of a sample to be examined.Firstly, this can ensure that use is made of a measuring tip with asufficient quality, i.e., with an appropriate radius of curvature of thetip of the measuring tip and with a matched aperture angle of themeasuring tip for analyzing the sample, and, secondly, this can ensurethat the outlay for generating the test structure and for examining themeasuring tip by use of the generated test structure remains withinreasonable levels.

The contour of the at least one test structure may be matched to theform of the measuring tip.

By way of example, the contour of the test structure can havesubstantially the same form as the original or prescribed form of themeasuring tip itself. This configuration eases the examination of themeasuring tip or of the current form of the measuring tip of an SPMand/or the determination of correction values for correcting themeasurement data recorded by the measuring tip for the purposes ofgenerating a realistic contour of the analyzed sample. A combination, inwhich the test structure may be matched both to the form of themeasuring tip and to a contour of the sample, is also conceivable.

Here and elsewhere in this application, the expression “substantially”denotes an indication of a measurement variable within its errortolerances when the measurement variable is measured using measuringinstruments in accordance with the prior art.

The contour of the at least one test structure can be embodied to detecta movement direction of the measuring tip that deviates from a samplenormal.

As a result, it is possible to identify and correct artifacts whendetermining a position of a defect or of a mark. The measurementaccuracy of the measuring tip of the SPM can be improved by virtue ofthe test structure allowing the determination of whether the movementdirection of the measuring tip has a deviation from the z-direction,i.e., from the sample normal. The effect of a non-perpendicular movementof the measuring tip can be taken into account when generating an imageof the measurement data generated by use of the scanning.

A movement of the measuring tip relative to a sample surface occurs in amode of operation in which a cantilever, to which the measuring tip hasbeen fastened, is made to vibrate, preferably at or in the vicinity of aresonant frequency of the cantilever. Further, a periodic relativemovement between sample and measuring tip occurs during a step-in modeof operation.

The contour of the at least one test structure can be embodied to detecta height-dependent lateral offset of a measuring tip, which comprises amovement direction of the measuring tip that deviates from the samplenormal.

The determination of this quantity is of particular importance when themeasuring tip is used to analyze the contour of a defect and the defectis repaired or compensated by use of a repair apparatus, wherein theimage of the defect or a mark by the scanning probe microscope isaligned with an image of the defect or the mark recorded by the repairapparatus.

The contour of the at least one test structure can be embodied to detecta measuring tip that is oriented at an angle that differs from zero withrespect to the sample normal, while the measuring tip carries out aperiodic movement parallel to the surface normal.

The contour of the at least one test structure can be embodied todistinguish between a movement direction of the measuring tip thatdeviates from the sample normal and a movement of the measuring tip inthe normal direction, wherein the measuring tip has an angle thatdiffers from zero with respect to the sample normal.

This property of the test structure allows a distinction to be made asto whether a lateral component, for instance in the x-direction or thefast scanning direction, has been added to the closed-loop control forthe z-direction when scanning the measuring tip over the test structureor whether an obliquely positioned measuring tip carries out a vibrationalong the sample normal. In the mode of operation specified first,better imaging of samples with protruding structure elements istypically achieved under the precondition that the oblique movement hasa movement component in the direction of the protrusion.

The contour of the at least one test structure can be embodied tomaximize a component of the measuring tip imaged by the at least onetest structure.

Such a test structure facilitates precise imaging of not only the tip ofthe measuring tip, but also of a portion of the entire surface of themeasuring tip that is as large as possible. If the geometry or the formof the entire measuring tip is known, the influence of the measuring tipon the measurement data of a scanning procedure can be determined to thebest possible extent and can be compensated when generating an image ofa scanned sample surface.

The test structure can be rotationally symmetric with respect to thesample normal. A cross section of the test structure can be ellipticalor polygonal. The test structure may comprise at least one column-likestructure with a conical tip, which ends in a hemispherical form.

The at least one test structure may comprise at least one tip with aradius of curvature of <100 nm, preferably <50 nm, more preferably <20nm and/or most preferably <10 nm and/or the at least one test structuremay comprise an aperture angle of <40°, preferably <30°, more preferably<20° and most preferably <10°.

The test structure may comprise at least one structure element with anundercut.

This property of the test structure allows the form of a measuring tipto be analyzed away from the tip thereof without the tip of themeasuring tip interacting with the test structure. This ensures aprecise examination of the measuring tip. Moreover, a suitably undercuttest structure can be used to examine the measuring tip of a CD AFM(critical dimension atomic force microscope).

The at least one test structure can be generated at a site of the sampleor of the substrate at which the at least one test structuresubstantially does not impair a function of the sample or of thesubstrate.

Generating the at least one test structure may comprise: providing afocused particle beam and at least one precursor gas at the site atwhich the at least one test structure is generated. The precursor gasfor depositing a test structure may comprise a metal carbonyl and/or ametal alkoxide. The metal carbonyl may comprise chromium hexacarbonyl(Cr(CO)₆) and/or molybdenum hexacarbonyl (Mo(CO)₆), tungstenhexacarbonyl (W(CO)₆), dicobalt octacarbonyl (Co₂(CO)₈), trirutheniumdodecacarbonyl (Ru₃(CO)₁₂) and iron pentacarbonyl (Fe(CO)₅). The metalalkoxide may comprise tetraethyl orthosilicate (TEOS) (Si(OC₂H₅)₄)and/or titanium isopropoxide (Ti(OCH(CH₃)₂)₄). Further precursor gasesfor depositing one or more test structures are specified in theapplicant's U.S. patent application Ser. No. 13/103,281.

Further, the at least one test structure may comprise carbon as a mainconstituent part. Such a test structure, which is deposited on aphotolithographic mask, for example, is advantageous in that the teststructure can be removed substantially without residue from the maskagain at the end of the mask production process or the mask repairprocess using standard cleaning methods. Precursor gases for depositingtest structures predominantly containing carbon are: ethene (H₂C₂),pyrene (C₁₆H₁₀), hexadecane (C₁₆H₃₄), formic acid (CH₂O₂), acetic acid(C₂H₄O₂), acrylic acid (C₃H₄O₂), propionic acid (C₃H₆O₂), methylmethacrylate (MMA) (C₅H₈O₂) and paraffins.

The particle beam may comprise an electron beam, an ion beam, a photonbeam, an atomic beam and/or a molecular beam. The at least one teststructure can be deposited with the aid of an electron beam-induceddeposition (EBID) process. An electron beam-induced deposition processis advantageous in that the employed electron beam causes no damage, orno substantial damage, to the sample to be examined.

Depositing and/or etching the at least one test structure may comprise:providing a focused particle beam and at least one etching gas at thesite of the at least one test structure. The etching gas may comprise:Xenon difluoride (XeF₂), xenon dichloride (XeCl₂), xenon tetrachloride(XeCl₄), water vapor (H₂O), heavy water (D₂O), oxygen (O₂), XNO, XONO₂,X₂O, XO₂, X₂O₂, X₂O₄, X₂O₆, where X is a halide, ammonia (NH₃) and/ornitrosyl chloride (NOCl). Further etching gases for etching one or moreof the deposited test structures are specified in the applicant's U.S.patent application Ser. No. 13/103,281.

Firstly, a local etching process allows deposited test structures to bematched to a sample to be examined and/or to a measuring tip whennecessary. This allows test structures to be generated, the structurequantities of which have dimensions that cannot be achieved with the aidof a deposition process. Secondly, a local etching process allows teststructures to be generated directly, for example by etching into asubstrate of a mask.

The at least one test structure can be generated on the sample when thesample is produced.

In another embodiment, the test structure is already produced on thesample during the production process of the latter. As a result, thetest structure can be matched individually to the structure elements ofa sample. Then, this individualized test structure is available duringthe service life of the sample in order to optimize the analysis of thesample with the aid of a measuring tip of an SPM by examining themeasuring tip employed for the analysis. However, the problems regardingwear and dirtying, as explained above, must be taken into account,particularly when the sample is operated outside of a vacuumenvironment.

Steps a. and b. can be carried out in vacuo without breaking the vacuum.

A scanning probe microscope is often applied in combination with ascanning particle microscope, for instance a scanning electronmicroscope. Typically, a scanning particle microscope operates in avacuum environment. The above-defined method is advantageous in that thescanning particle microscope may provide a focused particle beam fordepositing and/or etching the test structure, and so the sample does nothave to be replaced and the measuring tip does not have to beinterchanged for the purposes of depositing the test structure andexamining the measuring tip of the SPM. Since the SPM scans the samplein a vacuum environment, the deposited test structure is subjected tosubstantially no dirtying.

Examining the measuring tip may comprise: scanning the measuring tipover the at least one deposited test structure.

When scanning a measuring tip of an SPM over a sample or test structure,the measurement data of the SPM contain a superposition of the geometryor the form of the measuring tip and the contour of the sample or thecontour of the test structure. Mathematically, the superposition isdescribed by a convolution or convolution operator. The next paragraphspecifies citations that describe a convolution of a sample and themeasuring tip of an SPM. If a radius of curvature of the measuring tipand the aperture angle thereof are small in relation to the contour ofthe sample, the measurement data of a scanning procedure over the samplesubstantially image the contour of the sample. In the other limit case,when the contour of the sample has changes in the height profile thatare greater or very much greater than the form or geometry of themeasuring tip, the changes in the height profile of the samplesubstantially image the form of the measuring tip.

In order to prevent the case mentioned last, a test structure adopts thefunction of a reference normal, with the aid of which the measuring tipof an SPM can be examined in order to determine the geometry or formthereof. This means that the contour of the test structure should haveat least a similar size as the form of a measuring tip. However, it isbetter if the contour of the test structure has steeper changes than theform of the measuring tip of the SPM. On the basis of knowledge of theform of the measuring tip, the actual contour of a sample can be deducedfrom the measurement data from scanning said sample. This process orthis deconvolution process has already been described multiple times inthe literature, for example in the documents cited in the introductorypart: X. Qian et al.: “Image simulation and surface reconstruction ofundercut features in atomic force microscopy,” SPIE Proc. Vol. 6518,(2007), p. 1-12; L. Udpa et al.: “Deconvolution of atomic forcemicroscopy data for cellular and molecular imaging,” IEEE, Sig. Proc.Mag. 23, 73 (2006); J. S. Villarrubia: “Algorithms for scanned particlemicroscope image simulation, surface reconstruction, and tipestimation,” J. Res. Natl. Inst. Stand. Technol. 102, p. 425-454 (1997);G. Dahlen et al.: “Tip characterization and surface reconstruction ofcomplex structures with critical dimension atomic force microscopy,” J.Vac. Sci. Technol. B 23(6), November/December 2005, p. 2297-2303; and X.Qian and J. S. Villarrubia: “General three-dimensional image simulationand surface reconstruction in scanning probe microscopy using a dexelrepresentation,” Ultramicroscopy 1008 (2007), p. 29-42.

The deconvolution operation mathematically represents the reversal ofthe convolution operation. The deconvolution of the measurement data,which were generated by scanning the measuring tip of an SPM about ameaning of the influence of the measuring tip, becomes more important ifthe greatest changes in the height profile of the sample come into thevicinity of the form of the measuring tip or even exceed the latter.

Moreover, it is very important for a reproducible quantitativemeasurement of an SPM to know the changes in form of a measuring tip onaccount of wear and/or dirtying and to take this into account in theanalysis of the measurement data generated by the measurement tip forthe purposes of generating a contour of a sample surface.

Examining the measuring tip may comprise: Imaging the at least onedeposited test structure by way of a focused particle beam.

Preferably, the test structure on the sample and/or the substrate isgenerated by use of a particle beam-induced deposition process and/or byuse of a particle beam-induced etching process. As a result, a focusedparticle beam is typically available in an apparatus for carrying out amethod according to the invention. Said focused particle beam can beused to analyze whether the contour of the deposited test structurecorresponds to a predetermined contour. If there are deviationstherefrom, the deposited test structure can be modified with the aid ofa local etching process in such a way that the measured contour of saiddeposited test structure substantially corresponds to the predeterminedcontour.

Examining the measuring tip may further comprise: generating a map ofregions of the sample that cannot be reached by the measuring tip of thescanning probe microscope.

This map allows the region or regions of a sample in which the imagedata generated from the measurement data do not correctly reproduce theactual contour of the sample to be ascertained. The regions in which thecontour of the sample cannot be determined can be reduced or can be madeto virtually disappear by way of replacing the measuring tip with afiner measuring tip, i.e., with a smaller radius of curvature and/orwith a smaller aperture angle, and/or by scanning the measuring tip,wherein the movement of the measuring tip has a movement componentperpendicular to the sample normal and hence a lateral movementcomponent.

The method according to the invention may further include the step of:scanning the sample by a particle beam for finding a defect in thesample. A photon beam and/or an electron beam is preferably used foranalyzing a sample surface.

Further, the method according to the invention can include the step of:generating at least one mark on the sample for the purposes of findingthe defect by the measuring tip of the scanning probe microscope. The atleast one mark may comprise the at least one test structure.

Frequently, a mark is applied to a sample having one or more defects,which are analyzed by different types of metrology appliances. Themark(s) serve for easier identification of the regions to be analyzed bythe respective metrology appliance. Further, these mark(s) can be usedfor correcting the drift of the repair apparatus during a repairprocess. By virtue of these mark(s) being embodied in such a way thatthese additionally satisfy the function of a test structure for ameasuring tip of a scanning probe microscope, a test structure can becreated with minimal additional outlay in the direct vicinity of aregion of a sample to be analyzed. Moreover, this minimizes the outlayfor switching between an analysis of the sample with the measuring tipand examining the measuring tip of the SPM by use of the test structure.

Examining the measuring tip may comprise: determining a current form ofthe measuring tip on the basis of scanning the measuring tip over the atleast one deposited test structure. Further, examining the measuring tipmay comprise: comparing the current form of the measuring tip to apredetermined form of the measuring tip and/or comparing the currentform of the measuring tip to the contour of the sample.

The method according to the invention may further include the step of:scanning the sample with the measuring tip if the current form of themeasuring tip lies within a predetermined variation range in respect ofthe predetermined form of the measuring tip and/or if the current formof the measuring tip has a predetermined distance from the maximumchange in the height profile of the sample.

In addition, the method according to the invention can include the stepof: changing the measuring tip of the scanning probe microscope if thecurrent form lies outside the predetermined variation range in respectof the predetermined form. Changing the measuring tip may comprise:changing the measuring tip of the scanning probe microscope or usinganother measuring tip of a probe arrangement of the scanning probemicroscope.

Using a probe arrangement with two or more probes can firstly increasethe utilization of the individual measuring tips on the basis of thesample(s) to be analyzed by virtue of already worn measuring tips beingused for analyzing samples that have no great aspect ratio in theircontour. Secondly, the time interval between replacements of a probearrangement can be significantly lengthened in comparison with a probecontaining only a single measuring tip. The aspect ratio denotes theratio of the depth or height of a structure to its (smallest) lateraldimension.

Moreover, the method according to the invention can include the step of:cleaning and/or sharpening the measuring tip of the scanning probemicroscope if the current form lies outside the predetermined variationrange of the predetermined form. Cleaning and/or sharpening themeasuring tip of the scanning probe microscope may comprise: Irradiatingthe measuring tip with a focused particle beam. Moreover, cleaningand/or sharpening the measuring tip can comprise: providing an etchinggas at the site of the measuring tip.

An advantage of the described method is that the processes of sharpeningand cleaning a measuring tip can be carried out in an SPM without themeasuring tip having to be disassembled from the scanning probemicroscope to this end.

The step of sharpening and/or the step of cleaning can be repeated onceto ten times, preferably once to eight times, more preferably once tofive times, and most preferably once to three times.

Moreover, the method according to the invention can include the step of:depositing material on the tip of the measuring tip if the current formof the measuring tip lies outside of the predetermined variation rangeof the form of the measuring tip.

Depositing material on the tip of a worn measuring tip can restore theoriginal radius of curvature thereof and can hence significantlyincrease the service life of said measuring tip.

By way of example, a carbon-based, long, fine measuring tip, which isknown as a “whisker tip,” can be deposited on the measuring tip.

Finally, the method according to the invention can comprise the stepsof: (a) removing a measuring tip if the current form of the measuringtip lies outside of the predetermined variation range of the form of themeasuring tip and (b) depositing a new measuring tip. Step (a) can becarried out with the aid of an electron beam-induced and/or ionbeam-induced etching process.

The measures explained last can be carried out since the success thereofcan easily be checked on the basis of the continuously available teststructure, and so the influence of the repaired measuring tip, i.e., thesharpened or cleaned or newly produced measuring tip, on the measurementdata generated by the measuring tip is known at all times and can beremoved by calculation. As a result, the discussed measures facilitate adrastic lengthening of the time between two changes of a measuring tipin comparison with a scanning probe microscope whose measuring tipcannot be repaired.

The sample may comprise a photolithographic mask or a wafer. The atleast one test structure can be deposited on an edge of thephotolithographic mask, on which edge substantially no radiation at anactinic wavelength is incident. Further, the at least one test structurecan be deposited on an edge of a wafer between two chips.

The at least one test structure can be deposited on a pattern element ofthe photolithographic mask. In particular, the at least one teststructure can be deposited on an absorbing pattern element of thephotolithographic mask.

This embodiment is advantageous in that the distance between the teststructure and the region to be analyzed by the measuring tip of the SPMcan be kept small, simplifying an examination of the measuring tip atshort time intervals within an analysis process of the sample by themeasuring tip of the SPM.

In accordance with a further exemplary embodiment of the presentinvention, the problem mentioned above is solved by an apparatus forexamining a measuring tip of a scanning probe microscope. The apparatuscomprises: (a) a generation unit that is embodied for generating a teststructure before a sample is analyzed, or after said sample has beenanalyzed, by the measuring tip; and (b) an examination unit that isembodied to examine the measuring tip with the aid of the at least onegenerated test structure.

The generation unit can be embodied to deposit a test structure and/oretch a test structure.

The generation unit can be embodied to generate the at least one teststructure on the sample and/or on a substrate.

The apparatus according to the invention may further comprise adisplacement unit that is embodied to bridge a distance between a pointof incidence of a particle beam of the generation unit on the sampleand/or a substrate and an interaction location between the sample and/orthe substrate and the measuring tip.

Moreover, the apparatus according to the invention can be embodied tocarry out the method steps of the above-defined method according to theinvention and of the aspects specified above.

Finally, a computer system may comprise instructions that, when executedby a computer system of an apparatus, prompt a control device of theapparatus to carry out the steps of the above-defined method and of theaspects specified above

DESCRIPTION OF DRAWINGS

The following detailed description describes currently preferredexemplary embodiments of the invention, with reference being made to thedrawings, in which:

FIG. 1 shows a schematic representation of a probe of a scanning probemicroscope (SPM) in partial image A and reproduces a probe arrangementof a scanning probe microscope comprising two different measuring tipsin partial image B;

FIG. 2 schematically elucidates the course of a test of a measuring tipof an SPM and of a probe change according to the prior art;

FIG. 3 schematically represents a flowchart of a method according to theinvention, with the necessary method steps being highlighted;

FIG. 4 reproduces a plan view of a photolithographic mask in partialimage A on the left, with a section that should be sensed by a measuringtip of an SPM and that is illustrated in magnified fashion on the right,and presents in partial image B partial image A after attachment of atest structure to the edge of the photolithographic mask (left) or on apattern element (right);

FIG. 5 shows a schematic section through an apparatus for generating atest structure and for examining a measuring tip of an SPM with the aidof the previously generated test structure;

FIG. 6 reproduces a section through two embodiments of a test structure;

FIG. 7 presents sections and plan views of four further examples of teststructures;

FIG. 8 shows a section through two exemplary etched test structures;

FIG. 9 shows an unused measuring tip in partial image A, reproduces aworn measuring tip in partial image B, illustrates a contaminatedmeasuring tip in partial image C and shows a measuring tip repaired byan electron-beam-induced etching process in partial image D;

FIG. 10 represents the sensing of a section of a photolithographic maskwith an ideal measuring tip, oriented perpendicular to the maskednormal, in partial image A and specifies changes caused by realmeasuring tips in partial image B;

FIG. 11 repeats the sensing process of partial image A in FIG. 10, inwhich an ideal measuring tip oriented with respect to the sample or masknormal carries out an oblique or non-perpendicular movement with respectto the mask normal;

FIG. 12 repeats the sensing process of partial image A in FIG. 10, inwhich an ideal measuring tip, i.e., a measuring tip that has no lateralextent, carries out a movement along the mask normal and wherein theorientation of the measuring tip has an angle that differs from zerowith respect to the mask normal;

FIG. 13 elucidates sections of a sensing procedure over an embodiment ofa test structure which are carried out with different movement forms ofa measuring tip, wherein the test structure has two structure elementswith two indents or undercuts;

FIG. 14 reproduces the analysis of marks at different heights on patternelements of a mask section with the aid of an atomic force microscope(AFM) in the left partial image A and presents, in the right partialimage B, the section of the mask that was sensed with the aid of ascanning electron microscope (SEM); and

FIG. 15 represents a section of a scanning procedure of a measuring tipof a scanning probe microscope over a test structure specified in FIG.7, wherein the measuring tip carries out a movement deviating from thesample normal.

DETAILED DESCRIPTION

Below, currently preferred embodiments of a method according to theinvention for examining a measuring tip of a scanning probe microscope(SPM) are explained in more detail using the example of an atomic forcemicroscope (AFM). However, the method according to the invention is notrestricted to the application by an atomic force microscope. Rather, themethod according to the invention can be used for all types of scanningprobe microscopes, the measuring tips of which are subject to wear as aresult of interaction with a sample. Further, the defined method can beused for examining a measuring tip that is dirtied as a result ofscanning the measuring tip over a sample to surface.

Below, the method according to the invention is explained using theexample of an analysis of a photolithographic mask with a measuring tipof an AFM. However, the application of the method according to theinvention is not restricted to scanning over a photolithographic mask.By contrast, the method specified in this application can be used tooptimize the examination of all types of samples with the aid of ascanning probe microscope. Mentioned here purely by example is theanalysis of a wafer during various production steps of an integratedcircuit or semiconductor component. Finally, what should still bementioned at this juncture in exemplary fashion is that the measuringtip of an SPM can also be used for the purposes of processing a samplein addition to the analysis. There is an intensive interaction betweenthe measuring tip and a sample surface when processing a sample with theaid of a measuring tip of an SPM. Therefore, the measuring tip of an SPMis subject to increased wear and/or more pronounced dirtying during theprocessing of a sample. This means that the method according to theinvention can be used particularly advantageously for optimizing theprocessing process when processing a sample by a measuring tip of anSPM.

Upper partial image A in FIG. 1 shows a probe 150 of the scanning probemicroscope schematically and with great magnification. The probe 150comprises a cantilever 140, which ends in a holding plate 160 at oneend. With the aid of the holding plate 160, the probe 150 isincorporated into a measuring head of an SPM. By way of example, theholding plate 160 of the probe 150 can be used for fastening the probe150 to a piezo-actuator of an SPM (not illustrated in FIG. 1). The endof the cantilever 140 opposing the holding plate 160, or the free end ofsaid cantilever, carries a measuring tip 100 that ends in a tip 120. Themeasuring tip 100 can have any form. By way of example, the measuringtip 100 can have a pyramidal form or the form of a paraboloid ofrevolution. Further, the measuring tip 100 may have a flared-tip form(not illustrated in FIG. 1).

The cantilever 140 and the measuring tip 100 may be configured in onepiece. By way of example, the cantilever 140 and the measuring tip 100may be manufactured from a metal, for instance tungsten, cobalt oriridium, from a metal alloy, from a semiconductor, for instance silicon,or from an insulator, for instance silicon nitride. It is also possibleto manufacture the cantilever 140 in the measuring tip 100 as twoseparate components and to subsequently connect these to one another.This can be effectuated by adhesive bonding, for example.

In place of the probe 160 with a single measuring tip 100 and a singlecantilever 140, as illustrated in partial image A, the SPM can use ameasuring tip carrier or a probe arrangement 190, which has two or moremeasuring tips 100 and 110. A probe arrangement 190 is presentedschematically and with great magnification in the lower partial image Bof FIG. 1, said probe arrangement comprising five measuring tips 100 and110, which have different lengths and a different form. The measuringtip 100, which may be identical to the measuring tip 100 of the probe150, is attached to two cantilevers 140 of the probe arrangement 190 andthree cantilevers 140 of the measuring tip carrier 190 comprise themeasuring tip 110. Both measuring tips 100 and 110 are designed foranalysis purposes in the probe arrangement 190 of FIG. 1. It is alsopossible for each of the five cantilevers 140 of the probe arrangement190 to carry a measuring tip whose form is different and consequentlydesigned for a specific analysis of a sample (not reproduced in FIG. 1).Further, it is possible for the measuring tip carrier 190 tosimultaneously carry a number of measuring tips that are optimized foranalysis and processing purposes (not shown in FIG. 1).

The entire probe 150 is always replaced when a measuring tip 100 of theprobe 150 is changed. The probe arrangement 190 is replaced or there isa change from a worn and/or dirtied measuring tip 100, 110 to a lessworn or not worn and non-dirtied measuring tip 110, 100 when changingthe measuring tip 100, 110 of the probe arrangement 190.

When reference is made to a measuring tip 100, 110 below, no distinctionis made as to whether this measuring tip 100 is attached to a probe 150or a probe arrangement 190. Moreover, no distinction is made in respectof the specific form or geometry of this measuring tip 100, 110 and thetask for which the latter is designed.

FIG. 2 presents the course of a method for examining a measuring tip100, 110 of an SPM according to the prior art in exemplary fashion. Ifindications for the quality of the measuring tip 100, 110 not meeting apredetermined level of quality are detected while the measuring tip 100,110 is scanned over a sample, then there are two ways to handle thisnotification. Firstly, the measuring tip 100, 110 can be replacedwithout further analysis and the scanning procedure of the sample isthereupon continued with the new measuring tip. This may be particularlyexpedient if the scanning probe microscope uses a probe arrangement 190that comprises a plurality of measuring tips 100, 110.

In an alternative procedure, the measuring tip 100, 110 is removed fromthe SPM and analyzed in a specific test construction on the basis of thecommercially to available test body, which contains a test structure.Alternatively, the sample in an SPM can be replaced by the test body andthe measuring tip 100, 110 with questionable quality is measured bysensing the test structure of the test body. In the two alternativesspecified last, the quality of the measuring tip 100, 110 issubsequently determined and compared to a predetermined qualitythreshold. A measuring tip 100, 110 passing this test is used further.Should the analyzed measuring tip 100, 110 not meet the demanded qualitylevel, this measuring tip 100, 110 is replaced by a new measuring probeand the scanning procedure of the sample is continued or restarted witha new measuring tip.

FIG. 3 reproduces a flowchart 300 of a method according to theinvention. Method steps that are not mandatory are represented by adotted frame. These specify how the method according to the invention isembedded in an analysis process and serve to delimit the methodspecified in this application from the prior art explained in FIG. 2.The process steps essential to carrying out a method according to theinvention are highlighted by a solid, emboldened frame. In FIG. 4, someof the method steps are elucidated schematically in parallel using theexample of a sample in the form of a photolithographic mask 400.

The method begins with step 305. In a first step 310, a sample is sensedor scanned by the measuring tip 100, 110 of an SPM. A plan view of aphotolithographic mask 400 is shown schematically on the left in partialimage A of FIG. 4. The photolithographic mask 400, the photomask 400 orsimply the mask 400 has an edge 410 and an active surface 420. Unlikethe active region 420, the edge 410 comprises no pattern elements andtherefore does not serve to image structures into a photoresist, whichis disposed on a wafer. The mask 400 can be a transmitting or areflecting photomask 400. With the measuring tip 100, 110, a scanningprobe microscope senses a small section 430 of the photomask 400. Thesection 430 is illustrated in magnified fashion on the right in partialimage A. The section 430 of the photomask 400 comprises a substrate 440,on which three pattern elements 450 in the form of absorbing patternelements have been deposited. Further, the section 430 of the photomask400 comprises a defect 460, which is disposed on the substrate 440 ofthe mask 400. The defect 460 may comprise a depression in the substrate440, an elevation in the substrate 440 and/or the defect 460 maycomprise absorbing material that is deposited at a site on the substrate440 of the mask 400 that should be free from absorbing material. Thedefect 460 is typically the reason why the section 430 of the mask 400is sensed by the measuring tip 100, 110 of an SPM.

The measurement data generated by use of the sensing procedure themeasuring tip 100, 110 are evaluated parallel to the scanning procedureof the measuring tip 100, 110 over the section 430 of the mask 400.Here, an analysis carried out as to whether a contour of the sample,i.e., the aspect ratio of the pattern elements 450 and/or a height ordepth profile of the defect 460 of the section 430 of the mask 400, canbe examined with a predetermined form or geometry of the measuring tip100, 110. By way of example, this applies if the measuring tip 100, 110is designed to sense the aspect ratio of the absorbing pattern elements450 and/or the height or depth profile of the defect 460 in realisticfashion. If this does not apply, it is questionable whether the qualityof the measuring tip 100, 110 is sufficient to sense the contour of thesample, i.e., the pattern elements 450 and/or the height or depthprofile of the defect 460, in such a way that the measuring tip 100, 110of the SPM can reach all regions, or nearly all regions, of thesubstrate 440, of the pattern elements 450 and of the defect 460. If theanalyzed measurement data give rise to the fear that this condition isnot satisfied, indications are present that the quality of the measuringtip 100, 110 is insufficient for the analysis of the sample or the mask400. A decision is made in the decision block 310 as to whether theseindications are present, i.e., whether the quality of the measuring tip100, 110 is questionable.

If this does not apply and the measuring tip 100, 110 is suitable forsensing the section 430 of the photolithographic mask 400, a check iscarried out in decision block 360 as to whether the scan of themeasuring tip 100, 110 over the sample has been completed. If this isthe case, the method ends at step 365. However, if scanning of thesample not yet having been completed is determined in the decisionblock, the method returns to step 310 and continues the scanning orsensing of the sample or of the mask 400 using the measuring tip 100,110.

By contrast, if the quality of the employed measuring tip 100, 110 beingdoubtful is determined in decision block 310, the method advances tostep 315. In this step, a sample stage is displaced to a site at which atest structure can be deposited on the sample, for example the mask 400or a substrate. In the exemplary embodiment illustrated in FIG. 4, thisdisplacement can be implemented by displacement elements of a samplestage, which are able to displace a sample stage in the plane of thesample, i.e., in the xy-plane. The x-movement of the sample stage in thex-direction and/or the y-direction can be monitored by an interferometerfor each movement direction (cf. the description of FIG. 5).

A test structure is generated in the next step 320. Partial image B ofFIG. 4 specifies two exemplary embodiments for sites 470 and 480 on themask 400, at which a test structure can be generated. A test structurecan be generated by depositing a test structure on a sample and/or byetching a test structure into a sample. Details of a generation processof a test structure will be explained in the context of the discussionof FIGS. 5 and 6. Examples of test structures are specified in FIGS. 6,7 and 8. The left-hand diagram in partial image B shows an example of atest structure that is deposited on the edge 410 or the non-activeregion 410 of the photolithographic mask 400. The left-hand diagram inpartial image B presents the section 430 of the mask 400 that is alreadyillustrated in partial image A lying thereabove. A test structure isdeposited at the site 480 on the central pattern element of the patternelements 450 of the section 430 in partial image B.

In another exemplary embodiment, a test structure can be generated on asubstrate of an SPM (not shown in FIG. 4). As a substrate of an SPM, allcomponents of an SPM come into question that can be displaced in such away that a test structure placed on the substrate can be placed underthe measuring tip 100, 110 of the scanning probe microscope. Thus, inparticular, the sample stage and/or the sample holder of the SPM isqualified for being a substrate.

Again with reference to FIG. 3, the sample stage or the substrate isdisplaced in the next step 325 in such a way that the measuring tip 100,110 of the SPM can sense the test structure generated at the sites 470,480. To this end, the two aforementioned displacement elements of thesample stage can be used in the exemplary embodiment illustrated in FIG.4.

Thereupon, the measuring tip 100, 110 is examined in step 330 with theaid of the test structure generated at the site 470, 480. Details ofthis analysis process are discussed in the context of subsequent FIG. 6.

In process step 335, the present or current form of the measuring tip100, 110 is determined on the basis of the measurement data, which wereobtained when examining the measuring tip 100, 110 on the basis of thetest structure generated at the position 470, 480. This process step isexplained in greater detail below with reference to FIG. 6.

Whether the present or current form of the measuring tip 100, 110 lieswithin a predetermined variation range of a new or unused measuring tipis determined in decision block 340. Should this be the case, the methodreturns to step 310 and continues with the sensing of the sample, forexample the mask 400, with the measuring tip 100, 110 of the scanningprobe microscope.

By contrast, if the current form of the measuring tip 100, 110 fallsoutside of the to admissible variation range, the method continues withdecision block 345. A decision as to whether the measuring tip 100, 110should be repaired or replaced is made in decision block 345. If thedecision is in favor of repair, the measuring tip 100, 110 is repairedin step 350. A measuring tip 100, 110 can be repaired in four differentways, which are not shown in FIG. 3 for reasons of clarity. Firstly, themeasuring tip 100, 110 can be cleaned; secondly, the measuring tip 100,110 can be sharpened; thirdly, material can be deposited on themeasuring tip 100, 110 in order to bring the current form back withinthe admissible variation range with respect to the predetermined ororiginal form of the measuring tip 100, 110 and, finally, the presentmeasuring tip can be removed from the cantilever 140 and a new measuringtip 100, 110 can be deposited on the cantilever 140 at the site of theoriginal measuring tip.

Before the scanning procedure is continued with the repaired measuringtip in step 310, the method can jump back to step 330 from process step350 and the repaired measuring tip is examined with the aid of the teststructure deposited at the position 470, 480 in order to determinewhether the repair was successful. For reasons of clarity, this processstep is suppressed in the flow chart 300 in FIG. 3.

If the decision is to replace the measuring tip 100, 110 in decisionblock 345, the method proceeds to step 355, in which the currentmeasuring tip 100, 110 is replaced. Once again, the measuring tip 100,110 can be replaced in two ways, which are likewise not reproduced inthe flowchart 300 in FIG. 3 for reasons of clarity. Firstly, themeasuring tip 100 of the probe 150 can be replaced by a new measuringtip of an unused probe. Alternatively, a measuring tip 100, 110 of theprobe arrangement 190 can be replaced by a measuring tip 110, 100 thatis better suited to sensing the sample, for example the section 430 ofthe mask 400, than the previously used measuring tip 100, 110. Thepreviously used measuring tip 100, 110 of the probe arrangement 190still is available for scanning a sample, the contour of which has asmaller aspect ratio than the sample to be analyzed at the current time.

Finally, the method can jump back to process step 330 from step 355 in afurther step, likewise not represented in FIG. 3, and the measuring tip110, 100 of the probe arrangement 190 newly provided for use can beexamined prior to its use with the aid of the test structure depositedat 470, 480 in order to ensure that the measuring tip 110, 100 providedfor use has a form or geometry that is better suited to scanning thesample than the measuring probe 100, 110 originally used for thispurpose.

In an alternative embodiment, the quality of the measuring tip 100, 110of a test structure is always checked before a start of the examinationof a sample, for example the mask 400. In this procedure, the first stepof a method according to the invention is the generation of the teststructure. In a further modification, a measuring tip 100, 110 issubject to a quality control after a predetermined number of carried outmeasurement cycles. If the quality control is due, a test structure isgenerated on the sample and the current contour of the measuring tip100, 110 is determined with the aid of the generated test structure.

The essential differences between the conventionally used procedure forchecking the functionality of a measuring tip 100, 110, which isreproduced in FIG. 2, and the flow chart 300 of FIG. 3 defined in thisapplication are as follows: (a) The method reproduced in FIG. 3 requiresno probe or sample change. The time for introducing and removing a probe150 or test structure is dispensed with. (b) The test structuredeposited shortly before its use in situ 470, 480 is new and accordinglyhas no traces of wear. Further, the only just deposited test structureis substantially free from contaminations. Testing the functionality ofthe test structure and optionally carrying out a cleaning process forthe test structure are dispensed with.

The flowchart 300 presented in FIG. 3 can be carried out in an automatedprocess. This means that depositing a test structure, examining themeasuring tip 100, 110 and determining the current form of the measuringtip 100, 110 on the basis of the examination process of the measuringtip 100, 110 with the aid of the deposited test structure can beimplemented without human interaction.

FIG. 5 shows a schematic section through some important components of anapparatus 500, which can be used to carry out the method reproduced inFIG. 3. The apparatus 500 illustrated in FIG. 5 comprises a scanningprobe microscope 520 which, in an exemplary apparatus 500, is embodiedin the form of a scanning force microscope 520 or an atomic forcemicroscope (AFM) 520. Further, the exemplary apparatus 500 of FIG. 5comprises a modified scanning particle microscope 530, which is realizedas a modified scanning electron microscope (SEM) 530. As alreadymentioned above, the method described in this application canadvantageously be used for optimizing the use of a scanning probemicroscope 520, the measuring tip 100, 110 of which is subject to wearand/or dirtying as a result of an interaction with a sample.

The measuring head 523 of the scanning probe microscope 520 isillustrated in the apparatus 500 of FIG. 5. The measuring head 523comprises a holding apparatus 525. The measuring head 523 is fastened tothe frame of the apparatus 500 by use of the holding apparatus 525 (notshown in FIG. 5). The holding apparatus 525 can be to rotated about itslongitudinal axis which extends in the horizontal direction (not shownin FIG. 5). This allows the measuring tip 100, 110 to be placed underthe electron beam 535, wherein the tip 120, 130 of the measuring tip100, 110 points in the direction of the electron source 532. In analternative embodiment, the probe 150 or the probe arrangement 190 isput down in a probe store in the vacuum chamber of the apparatus 500. Amechanical unit, not shown in FIG. 5, rotates the measuring tip 100, 110about the longitudinal axis of the cantilever 140 and places saidmeasuring tip under the electron beam 535 of the SEM 530.

A piezo-actuator 515 which facilitates a movement of the free end of thepiezo-actuator 515 in three spatial directions (not illustrated in FIG.5) is attached to the holding apparatus 525 of the measuring head 523.Fastened to the free end of the piezo-actuator 515, there is a bendingbar 140 which is referred to as a cantilever 140 below, as isconventional in the art.

As illustrated in schematically magnified fashion in FIG. 1, thecantilever 140 comprises a holding plate 160 for attachment to thepiezo-actuator 515. In place of a single measuring tip 100 of the probe150, a measuring tip carrier 190 or a probe arrangement 190 may beattached to the measuring head 523 of the SPM 520, said measuring tipcarrier or probe arrangement comprising two or more measuring tips. Anexample of a probe arrangement 190 with five measuring tips 100, 110 isspecified in partial image B in FIG. 1.

In the apparatus 500 of FIG. 5, a sample 510 to be examined is fastenedto a sample stage 505. The sample surface 512 of the sample 510 to beexamined points away from the sample stage 505. By way of example, thesample 510 can be fixed by placing the sample 510 on the bearing pointsof the sample stage 505 in a vacuum or high vacuum environment or by anelectrostatic interaction between the sample stage 505 and anelectrically conductive rear side of the sample 510. Moreover, thesample 510 can be held on the sample stage 505 by clamping (not shown inFIG. 5).

The sample 510 may be any microstructured component or structural part.By way of example, the sample 510 may comprise a transmitting orreflecting photomask, for instance the photomask 400 of FIG. 4, and/or atemplate for nanoimprint technology. Furthermore, the SPM 520 can beused for examining for example an integrated circuit, amicroelectromechanical system (MEMS) and/or a photonic integratedcircuit.

As indicated by arrows in FIG. 5, the sample stage 505 can be moved by apositioning system 507 in three spatial directions relative to themeasuring head 523 of the AFM 520. In the example in FIG. 5, thepositioning system 507 is embodied in the form of a plurality ofmicromanipulators or displacement elements. The movement of the samplestage 505 in the sample plane, i.e., in the xy-plane, can be controlledby two interferometers (not shown in FIG. 5). In an alternativeembodiment, the positioning system 507 may additionally containpiezo-actuators (not illustrated in FIG. 5). The positioning system 507is controlled by signals of a control device 580. In an alternativeembodiment, the control device 580 does not move the sample stage 505,but rather the holding apparatus 525 of the measuring head 523 of theAFM 520. It is furthermore possible for the control device 580 toperform a coarse positioning of the sample 510 in height (z-direction)and for the piezo-actuator 515 of the measuring head 523 to perform aprecise height setting of the AFM 520. The control device 580 can bepart of a computer system 585 of the apparatus 500.

As an alternative or in addition thereto, in a further embodiment, it ispossible to divide the relative movement between the sample 510 and themeasuring tip 100, 110 between the positioning system 507 and thepiezo-actuator 515. By way of example, the positioning system 507performs the movement of the sample 510 in the sample plane (xy-plane)and the piezo-actuator 515 facilitates the movement of the measuring tip100, 110 or, in general, of the probe 150 or probe arrangement 190 inthe direction of the sample normal (z-direction).

As already mentioned, the exemplary scanning particle microscope 530 ofFIG. 5 contains a modified SEM 530. An electron gun 532 produces anelectron beam 535, which is directed as a focused electron beam 535 ontothe sample 510 at the location 545 by the imaging elements, notillustrated in FIG. 5, disposed in the column 537, said sample beingdisposed on a sample stage 505. Further, the imaging elements of thecolumn 537 of the SEM 530 can scan the electron beam 535 over the sample510. Further, the electron beam 535 can be directed on the sample stage505 or a sample holder (not shown in FIG. 5).

The electrons backscattered from the electron beam 535 by the sample,for example from the position 470 and/or 480, and the secondaryelectrons generated by the electron beam 535 in the sample 510, forinstance at the site 470 and/or 480, are registered by the detector 540.A detector 540 that is disposed in the electron column 537 is referredto as an “in lens detector.” The detector 540 can be installed in thecolumn 537 in various embodiments. The detector 540 is controlled by thecontrol device 580. Further, the control device 580 of the SPM 530receives the measurement data of the detector 540. The control device580 can generate images from the measurement data and/or the data of themeasuring head 523 or the measuring tip 100, 110, said images beingpresented on a monitor 590.

The control device 580 and/or the computer system 585 may furthercomprise one or more algorithms that prompt the apparatus 500 to deposita test structure at the position 470, 480. Further, the algorithm oralgorithms can act on the apparatus 500 in order to examine themeasuring tip 100, 110 with the aid of the deposited test structure.Moreover, the algorithm or algorithms can be designed to ascertain thecurrent form of the measuring tip 100, 110 from the generatedmeasurement data.

As an alternative or in addition thereto, the scanning probe microscope530 may have a detector 542 for backscattered electrons or for secondaryelectrons, said detector being disposed outside of the electron column537. The detector 542 is likewise controlled by the control device 580.

The electron beam 535 of the SEM 530 can be used to image the sample510. Moreover, the election beam 535 of the SEM 530 can also be used togenerate one or more test structures at the sites 470, 480 on the sample510 or the sample stage 505. A test structure can be generated bydepositing and/or etching a test structure. For the purposes ofgenerating a test structure and for carrying out further tasks, theapparatus 500 of FIG. 5 comprises three different supply containers 550,555 and 560.

The first supply container 550 stores a first precursor gas, inparticular a first carbon-containing precursor gas. By way of example, ametal carbonyl, for instance chromium hexacarbonyl (Cr(CO)₆), or a metalalkoxide, for instance TEOS, can be stored in the first supply container550. Further precursor gases that are suitable for depositing a teststructure with a high carbon content are specified in the third sectionof this description. With the aid of the precursor gas stored in thefirst supply container 550, a test structure 470, 480 can be depositedon the sample 510 or the mask 400 in a local chemical reaction, with theelectron beam 535 of the SEM 530 acting as an energy supplier in orderto split the precursor gas stored in the first supply container 550 atthe location at which the test structure 470, 480 should be deposited onthe mask 400. This means that an EBID (electron beam induced deposition)process for generating a test structure is carried out by the combinedprovision of an electron beam 535 and a precursor gas.

An electron beam 535 can be focused onto a spot diameter of a fewnanometers. As a result, an EBID process allows the deposition of teststructures having structure elements in the low two-digit nanometerrange. The combination of a scanning particle to microscope 530 and thecontrol device 580 is also referred to as generation unit 584. Further,the combination of a scanning probe microscope 520 and the controldevice 580 is also referred to as examination unit 582.

In addition to depositing a test structure 470, 480, an EBID process canalso be used for depositing material on the tip 120, 130 of a wornmeasuring tip 100, 110. As a result, a worn tip 120, 130 of a measuringtip 100, 110 can be sharpened again such that its form can be improvedat least to such an extent that the latter lies within a predeterminedvariation range of a new unused measuring tip.

Moreover, a local EBID process can be used to correct the defect 460 ifthe defect 460 is a defect of lacking material.

The second supply container 555 stores an etching gas, which makes itpossible to perform an electron beam induced etching (EBIE) process.With the aid of an electron beam-induced etching process, a teststructure deposited by use of an EBID process can be modified in such away that said test structure has a predetermined contour. A teststructure can be transferred by dragging a contamination of the sample510 on the test structure by the measuring tip 100, 110. As a result ofa cleaning process for the test structure 470, 480, the functionality ofthe latter can be substantially restored. To this end, the teststructure at the site 470, 480 is cleaned by an electron beam 535 and,optionally, under the provision of the etching gas stored in the secondsupply container 555.

Further, the electron beam 535 can be generated in combination with anetching gas for the purposes of generating a test structure by etching atest structure into a sample 510 and/or a sample stage 505

As mentioned above, the measuring tip 100, 110 of the SPM 520 can berotated about its horizontal axis. This renders it possible to clean adirtied measuring tip 100, 110 by way of irradiation with the electronbeam 535 and optionally by provision of a suitable etching gas, which iskept available in the supply container 555, for example.

If the defect 460 is a defect of excess material, the defect 460 can beremoved from the mask 400 by carrying out a local EBIE process. Anetching gas can comprise for example xenon difluoride (XeF₂), chlorine(Cl₂), oxygen (O₂), ozone (O₃), water vapor (H₂O), hydrogen peroxide(H₂O₂), dinitrogen monoxide (N₂O), nitrogen monoxide (NO), nitrogendioxide (NO₂), nitric acid (HNO₃), ammonia (NH₃) or sulfur hexafluoride(SF₆). Further suitable etching gases are listed in the third section ofthis description.

An additive gas can be stored in the third supply container 560, saidadditive gas being added to the etching gas kept available in the secondsupply container 555 or to the precursor gas stored in the first supplycontainer 550 where necessary. Alternatively, the third supply container560 can store a second precursor gas or a second etching gas.

The number of supply containers 550, 555, 560 in the apparatus 500 isnot set to three supply containers. The minimum number comprises asupply container for storing at least one precursor gas for depositing atest structure. Upwards, the number of supply containers of theapparatus 500 can be flexibly adapted to the process gases needed by theapparatus 500 for the processing processes to be carried out.

In the device 500 of FIG. 5, each of the supply containers 550, 555 and560 has its own control valve 551, 556 and 561 in order to monitor orcontrol the amount of the corresponding gas that is provided per unittime, i.e., the gas volumetric flow at the site 545 of the incidence ofthe electron beam 535 on the sample 510, on the sample holder or on themeasuring tip 100, 110. The control valves 551, 556 and 561 arecontrolled and monitored by the control device 580. This allows partialpressure conditions of the gases provided at the processing location 545for depositing a test structure at the position 470, 480 or forreleasing the further gases provided for the above-described processesto be set in a broad range.

Furthermore, in the exemplary apparatus 500 of FIG. 5, each supplycontainer 550, 555 and 560 has its own gas feed line system 552, 557 and562, which ends with a nozzle 553, 558 and 563 in the vicinity of thepoint of incidence 545 of the electron beam 535 on the sample 510, onthe sample stage 510 or on the measuring tip 100, 110.

In the example illustrated in FIG. 5, the valves 551, 556 and 561 aredisposed in the vicinity of the corresponding containers 550, 555 and560. In an alternative arrangement, the control valves 551, 556 and 561can be installed in the vicinity of the corresponding nozzles (not shownin FIG. 5). Unlike the illustration shown in FIG. 5 and withoutpreference at the present time, it is also possible to provide one ormore of the gases stored in the containers 550, 555 and 560non-directionally in the lower part 572 of the vacuum chamber 570 or thereaction chamber 572 of the apparatus 500. In this case, it would beexpedient for the apparatus 500 to have installed a stop (notillustrated in FIG. 5) between the lower reaction space 572 and theupper part 574 of the apparatus 500, which contains the column 537 ofthe SEM 530, which provides the focused electron beam 535, in order toprevent negative pressure that is too low in the upper part 574 of theapparatus 500.

The supply containers 550, 555 and 560 can have their own temperaturesetting to element and/or control element, which enables both coolingand heating of the corresponding supply containers 550, 555 and 560.This makes it possible to store and in particular provide thecarbon-containing precursor gas(es) and/or the etching gas(es) at therespectively optimum temperature (not shown in FIG. 5). Furthermore, thefeed line systems 552, 557 and 562 can comprise their own temperaturesetting elements and/or temperature control elements in order to provideall the processing gases at their optimum processing temperature at thepoint of incidence 545 of the electron beam 535 on the sample 510, onthe sample stage 505 if the test structure 470, 480 is deposited on thelatter or on the measuring tip 100, 110 (likewise not indicated in FIG.5). The control device 580 can control the temperature setting elementsand the temperature control elements both of the supply containers 550,555, 560 and of the gas feed line systems 552, 557, 562. When processingthe sample 510 by use of EBID and/or EBIE processes, the temperaturesetting elements of the supply containers 550, 555 and 560 can furtherbe used to set the vapor pressure of the precursor gases stored thereinby way of the selection of an appropriate temperature.

The apparatus 500 illustrated in FIG. 5 can be operated under ambientconditions or in a vacuum chamber 570. Depositing a test structure atone of the sites 470, 480 necessitates a reduced pressure in the vacuumchamber 570 relative to the ambient pressure. For this purpose, theapparatus 500 of FIG. 5 comprises a pump system 575 for generating andfor maintaining a reduced pressure required in the vacuum chamber 570.With closed control valves 551, 556 and 561, a residual gas pressure of<10⁻⁴ Pa is achieved in the vacuum chamber 570 of the apparatus 500. Thepump system 575 can comprise separate pump systems for the upper part574 of the apparatus 500 for providing the electron beam 535 of the SEMand for the lower part 572 or the reaction chamber 572 (not shown inFIG. 5).

Conventionally, test structures are typically generated on test bodiesby use of production methods that are known from the field of producingsemiconductor components. As a result of these production methods,significant restrictions arise in respect of the contour of the teststructure. As a result, the geometry of the measuring tip 100, 110 of anSPM 520 can only be determined incompletely. Most of these restrictionsare avoided by producing a test structure with the aid of an EBID and/orEBIE process, which is carried out by the apparatus 500. Additionally,an EBID process facilitates flexible matching of a test structure to theform of the measuring tip 100, 110 used by the SPM 520.

In partial image A, FIG. 6 shows a section through an embodiment of atest structure 600. The test structure 600 comprises a cylindrical shaft610, which is adjoined by a conically tapering tip region 620 that endsin a hemispherical tip 630. As explained above in the context of FIG. 5,the test structure 600 can be deposited from a carbon-containingprecursor gas, which is stored in the supply container 550 in theexemplary apparatus 500. The shaft 610 may have a diameter that rangesfrom the single-digit micrometer range down to the three-digit nanometerrange. The length of the shaft 610 of the test structure 600 typicallyhas similar dimensions. The aperture angle α 640 of the tip region 620ranges from 40° to approximately 10°. The radius of curvature of the tip630 ranges from 100 nm down to the single-digit nanometer range. For thepurposes of depositing the shaft 610, the focused electron beam 535 isfocused at the site 470, 480 at which the test structure should bedeposited, while the precursor gas is provided at the same time. Thecontour or geometry of the generated test structure depends on the spotdiameter in the focus, on the kinetic energy of the electrons of theelectron beam 535, on the current intensity and the irradiation time ofthe electron beam 535 and on the gas pressure of the employed precursorgas.

A test structure 600 predominantly comprising carbon is advantageous inthat the test structure 600 can be removed from the mask 400 again byuse of a conventional cleaning process at the end of a mask productionor mask repair process. This opens up the possibility of depositing thetest structure 600 not only on absorbing pattern elements 450 of themask 400 but also on phase-shifting pattern elements or on the substrate430 of a mask 400. Moreover, a test structure predominantly comprisingcarbon can be used in general for optimizing the examination of opticalelements with the aid of an SPM 520, which optical elements have nopattern elements 450.

In another embodiment, it is possible to deposit permanent teststructures 600 on the sample 510 or on a substrate with the aid of theSPM 520. To this end, for example, the precursor gas TEOS can be storedin the first supply container 550. The permanent test structure 600 canremain on the sample 510 and can be used, during the service life of thesample 510, by other scanning probe microscopes for optimizing theexamination of the sample 510 with an SPM 520. In a further embodiment,the test structure 600 can already be deposited at the position 470 or480 during the production of the sample 510 (not illustrated in FIG. 6).

The test structure 600 of FIG. 6 substantially has the form of themeasuring tip 100, 110. Should the contour of the test structure 600 andthe form or geometry of the measuring tip 100, 110 be substantiallyidentical, the deconvolution process for determining the form of themeasuring tip 100, 110 from sensing the test structure 600 with ameasuring tip 100, 110 is simplified. As explained in the third sectionof this description, the deconvolution process is already described inmany documents. Therefore, a presentation of this process here isdispensed with. Instead, reference is made to the documents listedabove.

The test structure 600 of FIG. 6 is rotationally symmetric. However,this is not necessary. Rather, the cross section of a test structure 600can be elliptical or polygonal. By way of example, a test structure 600can have a pyramidal structure (not shown in FIG. 6).

Partial image B of FIG. 6 presents a section through a test structure650, in which a plurality of the test structures 600 reproduced inpartial image A are combined. The elements 660 of the test structure 650are substantially identical to the test structure 600 of partial imageA. The elements 670 merely differ from the test structure 600 by virtueof a greater length of the shaft 610 of the test structure 600. The teststructure 650 of partial image B of FIG. 6 is deposited at one of thesites 470 and/or 480 on the mask 400 or on the sample 510 in an EBIDprocess, similar to the test structure 600.

In order to generate a test structure 650 whose structure elementsdiffer in a plurality of properties, it is possible to generate elements660 and 670 which have different radii of curvatures and/or differentaperture angles in addition to a different lengths of their shafts 610.As a result, it is possible to deposit a test structure 650 that issuitable for examining measuring tips 100, 110 whose original forms orgeometries are designed for analyzing different samples 510 andaccordingly have different forms. Moreover, it is expedient to have atest structure 650 with a plurality of different structure elements forexamining worn and/or dirtied measuring tips 100, 110.

Following the production of the test structures 600 and 650, these canbe imaged with the aid of the electron beam 535 of the SEM 530 in orderto check that the geometry or the contour of the test structures 600 and650 in fact has the intended form.

FIG. 7 schematically represents further examples of test structures 710,730, 750 and 770. The upper row of FIG. 7 shows sections through thetest structures 710, 730, 750 and 770 while the lower row reproducesplan views of the test structures 710, 730, 750 and 770. The teststructure 710 has two structure elements 715, 720, which have tipregions with the same contour but which differ in terms of the length oftheir shafts. As explained below, the test structure 710 is suitable fordetecting a lateral offset to within the scope of determining a positionof the measuring tip 100, 110, which lateral offset is caused by anoblique movement of the measuring tip 100, 110.

The test structure 730 comprises a shaft 735 with two indented orundercut structure elements 740 and 745, wherein the structure element745 disposed at the tip of the test structure 730 has a greater diameterthan the structure element 740 situated therebelow. The test structure730 allows a clear identification as to whether deviation of themovement of the measuring tip 100, 110 with respect to the sample normalexceeds a limit value. Overall, the test structures 710 and 730 aredesigned to detect the movement direction of a vibrating measuring tip100, 110 or of a measuring tip operated in the step-in mode ofoperation.

Indented structure elements 740, 745 can be produced by suitableguidance of the electron beam 535. If the area irradiated by theelection beam is increased during the production of the test structure730, undercut or indented structure elements 740, 745 are formed. Thearea exposed by the electron beam 535 can be increased by virtue ofincreasing the spot diameter of the electron beam 535 on the teststructure 730 or by virtue of moving a spot diameter of the focus withan unchanged size in a lateral direction.

The test structure 750 of FIG. 7 was deposited in the form of a conewith a bend 760 along the side face 755. Moreover, the test structure750 has a tip with a defined radius of curvature.

Finally, the exemplary test structure 770 of FIG. 7 comprises fivesubstantially identical, needle-shaped structure elements 780.Typically, the length of the structure elements 780 is shorter than thelength of the measuring tip 100, 110. The radius of curvature of themeasuring tip 100, 110 can be determined with the aid of the radii ofcurvature of the needle-shaped structure elements 780 of the teststructure 770. Moreover, whether the measuring tip 100, 110 reaches thebase between two of the structure elements 780 can be determined on thebasis of the test structure 770. Should this be the case, the diameterof the measuring tip 100, 110 is smaller than the distance betweenadjacent structure elements 780 of the test structure 770. In analternative embodiment, the distance and the length of the structureelements 780 of the test structure 770 can be varied in order to designthe test structure 770 for analyzing various forms of the measuring tips100, 110.

Ideally, the test structures 600, 650, 710, 730, 750 and 770 should haveperfect contours. This means that the shafts 610 of the structureelements 560, 570, 715, 720, 780 of the test structures 600, 650, 710,730, 750, 770 should be perpendicular and the to aperture angles of thestructure elements and their radii of curvatures should be small inrelation to the dimensions of the corresponding elements of themeasuring tip 100, 110. However, there are physical restrictions on theproduction of structure elements 560, 570, 715, 720, 740, 745, 780 fortest structures 650, 710, 730, 770.

An option for circumventing these restriction lies in the deposition ofa test structure 600, the contour of which comes as close as possible tothe form or geometry of the employed measuring tip 100, 110. This ispresented in partial figure A of FIG. 6. A second option forcircumventing the production restrictions exploits the production timeand the production type for the production structure. When depositingthe test structure 600, 650, 710, 730, 750, 770, for example at theposition 470 and/or 480, the original form or geometry of the measuringtip 100, 110 used by the SPM 720 is known. Moreover, depositing the teststructure 600, 650, 710, 730, 750, 770 in situ facilitates theadaptation of the test structure to the form or geometry of themeasuring tip 100, 110 to be examined. Using this, it is possible todesign, in particular, the arrangement of the structure elements 560,570, 715, 720, 735, 740, 745, 780 on the test structure in addition totheir form in such a way that the arrangement thereof can be exploitedto the best possible extent for the examination of the measuring tip100, 110.

FIG. 8 shows schematic sections through two examples of test structures810 and 850, which were etched into a sample 510. By way of example, thesample 510 may comprise the photomask 400. This means that the teststructures 810 and 850 can be etched into the edge 410 of the photomask400, for instance at the position 470. It is also possible to etch thetest structures 810 and 850 into a pattern element 450 of a photomask450, for instance at the position 480. However, the case specified lastassumes the pattern elements 450 are thick enough so that the residualthickness of the pattern element 450 still remaining after etchingsubstantially does not impair the function of said pattern element.

Five depressions 815, 820, 825, 830, 835 are etched into the sample 510in the test structure 810 of the upper partial image A in FIG. 8. Thedepressions 815, 820, 825, 830, 835 have different diameters andsubstantially the same depth. The depressions 815, 820, 825, 830, 835preferably have a rectangular, square or round form in the planeparallel to the sample surface 512. The test structure 810 representsthe counterpart to the test structure 770, with the difference that thedepressions of the test structure 810 have different diameters. It isalso possible to etch into a sample a test structure whose depth, whosediameter and/or whose forms differ, provided the dimensions are known.Further, two or more substantially identical test structures 810 to canbe etched successively into a sample in order to always have available anon-worn and/or non-dirtied test structure 810 when required.

The test structure 850 of the lower partial image B comprises adepression 855, the side walls 870 and 880 of which do not form a rightangle with respect to the sample surface 512. The sharp edges 860 of thetest structure 850 can be used, alone or in combination with the lowerside walls 880, for determining the contour and/or the radius ofcurvature of the measuring tip 100, 110.

The test structures 810 and 850 can be generated with the aid of theelectron beam 535 of the SEM 530 of the apparatus 500 and one of theetching gases stored in the supply container 555, i.e., can be generatedby use of an EBIE process. Etching gases suitable to this end are listedabove.

The repair of a worn or dirtied measuring tip 100, 110 is discussed onthe basis of FIG. 9. Partial image A presents a measuring tip 100, saidmeasuring tip being new or the tip 120 of which having substantially notraces of wear that can be traced back to an interaction with a sample400, 510. In the case of the used measuring tip 910 of partial image B,the tip 920 thereof has clear traces of use, which result in visiblewear in comparison with the original tip 120. Partial image C likewiseshows a used measuring tip 930. The tip 940 of the measuring tip 930 wasonly slightly rounded by the interaction with a sample 400, 510 andtherefore subjected to little wear. However, a particle 950 has beendeposited on the tip 940 of the measuring tip 930. The particle 950changes the measurement data of the measuring tip 930 for a samplesurface 512 in comparison with the new or substantially unworn measuringtip 100 of partial image A. However, it is also possible for the tip ofa used measuring tip 910, 930 to both have a worn tip 920 and be dirtied(not illustrated in FIG. 9).

The damage to the measuring tips 910 and 930 of partial images B and Ccan be repaired by a local electron beam-induced etching process usingthe electron beam 535 of the SEM 530 and an etching gas, which is storedin the supply container 555. Partial image D illustrates the repairedmeasuring tip 960. The contour of the tip 970 of the repaired measuringtip 960 is substantially the same as the contour of the tip 120 of thenew, i.e., unused, measuring tip 100. Consequently, the repairedmeasuring tip 960 supplies substantially the same measurement data asthe new measuring tip 100. The only difference between the two measuringtips 100 and 960 lies in the slightly shorter length of the repairedmeasuring tip 960. It is an important advantage of the discussed repairprocess for the measuring tip 100, 110 that—as explained in the contextof FIG. 3—it is possible to use the test structure 600, 650, 710, 730,750, 770, 810, 850 in order to check, without great outlay, that therepair process has in fact yielded the intended result.

Further problems that can be solved by depositing an appropriate teststructure 710, 730, 810, 850 in situ on a sample 400, 510 or the samplestage 505 are explained below. Partial figures A and B of FIG. 10illustrate a section of the photolithographic mask 400. The photomask400 comprises a substrate 440 and absorbing pattern elements 450. Thewidth of the pattern elements 450 is denoted by the double-headed arrow1020 and the height of said pattern elements is denoted by thedouble-headed arrow 1010. Typical values for both quantities lie in thetwo-digit to three-digit nanometer range.

In partial image A, an ideal needle-shaped measuring tip 1040, whichmoves perpendicular to the sample surface 512, senses the mask 400. Themovement direction of the ideal, arbitrarily thin measuring tip 1040 issymbolized by the double-headed arrow 1050. The line 1030 specifies thecontour that the measuring tip 1040 generates of the mask 400 or thesurface thereof.

Partial image B of FIG. 10 presents the contour of the mask 400, whenthe latter is sensed by real measuring tips 1070 or 1080. Here themeasuring tips 1070 and 1080—similar to the ideal measuring tip 1040 ofpartial image A—move in the z-direction, i.e., parallel to the normal ofthe mask 400. The measuring tip 1070, which is asymmetrical with respectto the longitudinal axis of the measuring tip 1070, generates anasymmetric contour 1060 of the mask 400. Additionally, regions of thesample surface 512 or of the surface of the mask 400 that cannot bereached by the measuring tips 1070 and 1080 arise due to the finiteextent of the measuring tips 1070 and 1080. In partial image B of FIG.10, these are the regions 1090 and 1095. The measuring tips 1070 and1080 cannot obtain any information about the contour of the sample 400,510 from the regions 1090 and 1095. The control device 580 or thecomputer system 585 of the apparatus can generate a map from the regions1090 and 1095, said map labeling the parts of the sample 400, 510 wherethe measuring tip 100, 110 of the SPM 520 cannot interact with thesample 400, 510.

FIG. 11 elucidates the sensing of the photomask 400 using the idealmeasuring tip 1040 of partial image A of FIG. 10. However, in contrastto partial image A of FIG. 10, the measuring tip 1040 does not carry outany movement in the z-direction. Instead, the oblique movement 1150 ofthe measuring tip 1040 deviates from the perpendicular or the normaldirection by the angle φ. In the example illustrated in FIG. 11, thelateral movement of the ideal measuring tip 1040 arises from a curvatureof the cantilever 140 toward the sample surface 512. The tip 120 of themeasuring tip 1040 carries out a complicated movement. The two referencesigns 1160 and 1170 specify the position of the measuring tip 1040 atthe two reversal points of the vibrations of the cantilever 140. Thecurvature of the cantilever 140 or the movement direction 1150 of themeasuring tip 1040 yields a deviation of the measured contour, dependingon the height of the pattern element 450 and being represented by thecurve 1110 in FIG. 11, from the actual contour of the pattern element:δ=h·tan φ≈h·φ.

In FIG. 12, the ideal measuring tip 1040 senses the photomask 400 or asection thereof using a perpendicular movement 1050. Unlike in partialimage A of FIG. 10, the measuring tip 1040 however has an angle withrespect to the surface normal that differs from zero. The curve 1230presents the regions in which the tip 120 of the ideal measuring tip1040 reaches the surface of the mask 400 and the regions in which thisis not the case. The curve 1210 specifies the contour of the mask 400which is generated by the obliquely positioned measuring tip 1040 by wayof carrying out a movement in the z-direction of the sample 510 or themask 400.

What can be gathered from the comparison of the curves 1110 and 1210 ofthe exemplary movement forms of the tip 120 of the measuring tip 1040illustrated in FIGS. 11 and 12 is that two different movements 1150 and1050 of an ideal measuring tip 1040 may lead to a substantiallyidentical contour of the mask 400. This is very disadvantageous as thisambiguity makes interpretation of the measurement data generated by useof the scanning probe microscope 520 significantly more difficult. Inreality, this situation is made even more complicated by the fact thatthe effects of the real measuring tip 1070 or 1080, discussed in partialimage B of FIG. 10, are still superposed on the contours 1110 and 1210.

FIG. 13 elucidates how a decision can be made with the aid of the teststructure 730 of FIG. 7 as to which form of movement the measuring tip1040 carried out when recording the measurement data in FIGS. 11 and 12.Partial figure A of FIG. 13 shows the sensing of the twice undercut teststructure 730 using a measuring tip 100, the associated cantilever 140of which carries out a vibration in the z-direction 950. The right-handside specifies the measured contour 1310, which is yielded by sensingthe test structure 730 with this movement form of the measuring tip. Thesymmetry of the test structure 730 and of the sensing process isreflected in the symmetry of the contour 1310.

On the left, partial image B of FIG. 13 presents the scanning of themeasuring tip 100 over the test structure 730, wherein the measuring tip100 carries out a vibration in the z-direction and, at the same time,has an angle with respect to the movement direction 1050, i.e., thez-direction, that differs from zero. A first option for carrying outsuch a movement of the measuring tip 100 requires the AFM measuring head523 being tilted. For a second option, the cantilever 140 of the probe150 or of the probe arrangement 190 is embodied as a bimetal. Thecantilever 140 warps as a result of an asymmetric photothermal actuationof the cantilever 140 with respect to its longitudinal axis, as a resultof which there is a change in the orientation of the measuring tip 100with respect to the surface normal. A photothermal actuation of thecantilever 140 can be carried out by irradiation with a laser beam. Themeasured contour 1320 of the test structure 730, which generates thismovement of the measuring tip 100, 110, is illustrated on the right-handside of partial image B. The asymmetry between orientation of the teststructure 730 and the measuring tip 100, 110 is uncovered by way of anon-symmetric contour 1320.

Finally, partial image C of FIG. 13 shows a scanning procedure of themeasuring tip 100 over the test structure 730, in which the movement1350 of the measuring tip 100 is carried out parallel to the orientationof the measuring tip 100 and wherein both are inclined by an angle inrelation to the z-direction or the sample normal. The contour 1330 ofthe test structure 730 generated by use of this scanning procedure isspecified to the right in partial image C. An asymmetric measuredcontour 1330 of the test structure 730 arises from the sensing procedureon account of the non-symmetrical movement of the measuring tip 100 withrespect to the test structure 730. The movement 1350 of the measuringtip 100 away from the vertical line of symmetry of the test structure730, i.e., at an angle with respect to the z-direction, however onlyfacilitates the detection of the second undercut structure element 740,which is expressed in the bend 1360 in the contour 1330 of the teststructure 730.

Consequently, sensing the test structure 730 using the movement formsillustrated in partial images B and C allows discrimination as to whichmovement the measuring tip 100, 110 carried out when scanning thecontours 1110 and 1210 of FIGS. 11 and 12. Consequently, the teststructure 730 allows the ambiguity arising in FIGS. 11 and 12 to beresolved and allows the contours 1110 and 1210 of the sample 510 or ofthe mask 400 to be unambiguously linked to the forms of movement carriedout by the measuring tip 100.

FIG. 14 and table 1 below illustrate a topic that may occur during thesuperposition of AFM and SEM images. The left partial image A of FIG. 14shows an AFM image of a section of a photomask 400, which comprises asubstrate 440 and pattern elements 1410, 1415, 1420 and 1425. One mark1450 is deposited on the pattern element 1415. Two marks 1430 and 1440are deposited on the pattern element 1420. The marks 1430, 1440 and 1450may have been deposited with the aid of an EBID process using theapparatus 500 of FIG. 5. The deposited marks 1430, 1440 and 1450 havedifferent heights. The marks 1430 and 1440 have a similar height of 66nm and 65 nm, respectively. The mark 1450 of the pattern element 1415has a height of 46 nm. The height of the markings 1430, 1440 and 1450was ascertained by sensing the markings using the measuring tip 100, 110of an SPM 520.

The markings 1430, 1440 and 1450 can be embodied as a test structure600, 650, 710, 730, 750, 770, 810, 850 (not shown in FIG. 14). At thesame time, the markings 1430, 1440 and 1450 serve to align the AFM image(partial image A) with an SEM image (partial image B) or, generally,with a scanning particle beam image. The two images are superposed inone application example in order to set the position of a defect 460 inthe SEM image for the purposes of repairing the defect 460 with the aidof the SEM 530 of the apparatus 500 of FIG. 5. Additionally, themarkings 1430, 1440 and 1450 can be used for correcting the drift of theSEM 530 during a correction of the defect 460.

Partial image B presents the section of the mask 400 of partial image A,which was imaged with the electron beam 535 of the SEM. In the partialimages A and B, double-headed arrows 1, 2 and 3 denote measurementswhich were carried out with the measuring tip 100, 110 of the probe 150or probe arrangement 190 of the SPM 520 in partial image A and with theelectron beam 535 of the SEM 530 in partial image B. The measurementdata are summarized in the following table.

TABLE 1 Height No. of the Distance of the Distance measurement AFM [nm]marking [nm] SEM [nm] Note 1 216 216 Set equal (reference) 2 265 66(1330) 266 Good 65 (1340) correspondence 3 239 65 (1340) 229 Poor 46(1350) correspondence

The first measurement serves to determine a reference or referencedistance between the AFM image and the SEM image. To this end, thedistance of two pattern elements is ascertained both with the SPM 520and with the SEM 530. In the example illustrated in FIG. 14, this is thedistance between the pattern elements 1415 and 1420.

In the second measurement, the distance between the markings 1430 and1440 is measured both by sensing the markings 1430 and 1440 with themeasuring tip 100, 110 and by scanning the electron beam 535 of the SEM530 over the markings 1430 and 1440. The values measured for thedistance between the two markings 1430 and 1440 differs by less than0.5%.

The third measurement is carried out in order to determine the distancebetween the markings 1440 and 1450 with the SPM 520 and the SEM 530 ofthe apparatus 500. As may be gathered from the last line of table 1, thedifference in the measurement results for the distance between themarkings 1440 and 1450 from the two metrology appliances lies between 4%and 5%, and hence it is significantly greater than for the secondmeasurement.

FIG. 15 uncovers the reason for the great difference in the measurementresults between the second and the third measurement in table 1. FIG. 15once again shows the mask 400, on which the test structure 710 of FIG. 7has been deposited at the position 470 and/or 480. The test structure710 has two structure elements 715 and 720, the heights of which differ.The double-headed arrow 1510 in FIG. 15 specifies the distance betweenthe two structure elements 715 and 720 of the test structure 710. Thedistance 1510 is measured when sensing the test structure 710, forexample with the electron beam 535.

The distance 1510 would also be measured by scanning the SPM 520 overthe test structure 710 if the structure elements 715 and 720 thereofwould have the same height, to be precise independently of the movementdirection of the measuring tip 100, 110 of the SPM 520 (cf. themeasurement No. 2 in table 1). Further, the SPM 520 would substantiallymeasure the distance 1510 between the structure elements 715 and 720 ofthe test structure 710 if the movement of the measuring tip 100, 110when sensing the test structure 710 is implemented parallel to thesample normal, i.e., in the z-direction.

The curve 1550 of FIG. 15 shows the contour of the test structure 710that arises if the measuring tip 100 carries out a vibration 1560 whenscanning the test structure 710, the direction of said vibration havingan angle with respect to the sample normal that differs from zero. Thedistance 1520 between the structure elements 715 and 720 of the teststructure 710 is ascertained from the contour 1550. The distance 1520measured by the SPM 520 is greater than the actual distance 1510 and isafflicted to by a systematic error. A non-perpendicular movement of themeasuring tip 100 in combination with different heights of the structureelements 715 and 720 of the test structure 710 leads to aheight-dependent lateral offset of the measurement of an SPM 720. Thisheight-dependent lateral offset explains the large difference in themeasurements in the last row of table 1.

By depositing a suitable test structure, for example the test structure710 that comprises two structure elements 715 and 720 with differentlengths or heights, it is possible to analyze the effect of the movementof the measuring tip 100, 110 on the measurement data generated by anSPM 520; i.e., the systematic error of a height-dependent lateral offsetcan be calculated and the measurement can be corrected accordingly.

In a manner similar to the example explained above, the furtherapplication example described in the context of FIGS. 14 and 15 showsthat test structures 600, 650, 710, 730, 750, 770, 810, 850, in additionto examining the measuring tip 100, 110 in respect of wear and/orcontamination, can also be used for the detailed analysis of themovement carried out by the measuring tip 100, 110 during a procedure ofsensing a sample 400, 510.

What is claimed is:
 1. A method for examining a measuring tip of ascanning probe microscope, wherein the method includes the followingsteps: a. generating at least one test structure before a sample isanalyzed, or after said sample has been analyzed, by the measuring tip,wherein generating the at least one test structure is carried out on thesample and/or a sample stage, and wherein generating the at least onetest structure comprises a particle beam-induced deposition of the teststructure and/or a particle beam-induced etching of the at least onetest structure; and b. examining the measuring tip with the aid of theat least one test structure deposited and/or etched on the sample and/orthe sample stage with the aid of the particle beam.
 2. The method ofclaim 1, wherein a contour of the at least one test structure is matchedto a contour of the sample.
 3. The method of claim 2, wherein thecontour of the at least one test structure is matched to the form of themeasuring tip.
 4. The method of claim 2, wherein the contour of the atleast one test structure is embodied to detect a movement direction ofthe measuring tip that deviates from a sample normal.
 5. The method ofclaim 1, wherein the test structure comprises at least one structureelement with an undercut.
 6. The method of claim 1, wherein the at leastone test structure is generated at a site of the sample or of the samplestage at which the at least one test structure substantially does notimpair a function of the sample or the sample stage.
 7. The method ofclaim 1, wherein generating the at least one test structure comprises:providing a focused particle beam and at least one precursor gas at thesite at which the at least one test structure is generated.
 8. Themethod of claim 1, wherein the at least one test structure is generatedon the sample when the sample is produced.
 9. The method of claim 1,wherein steps a. and b. are carried out in vacuo without breaking thevacuum.
 10. The method of claim 1, wherein examining the measuring tipfurther comprises: scanning the measuring tip over the at least onedeposited and/or etched test structure.
 11. The method of claim 1,wherein examining the measuring tip further comprises: imaging the atleast one deposited and/or etched test structure by way of a focusedparticle beam.
 12. The method of claim 1, further including thefollowing step: scanning the sample by a particle beam for finding adefect in the sample.
 13. The method of claim 12, further including thestep of: generating at least one mark on the sample for the purposes offinding the defect by the measuring tip of the scanning probemicroscope.
 14. The method of claim 13, wherein the at least one markcomprises the at least one test structure.
 15. The method of claim 1,wherein the sample comprises a photolithographic mask or a wafer. 16.The method of claim 15, wherein the at least one test structure isgenerated on an edge of the photolithographic mask, on which edgesubstantially no radiation at an actinic wavelength is incident.
 17. Themethod of claim 14, wherein the at least one test structure is generatedon a pattern element of the photolithographic mask.
 18. An apparatus forexamining a measuring tip of a scanning probe microscope, comprising: a.a generation unit that is embodied for particle beam-induced depositionand/or etching of a test structure on or in a sample and/or on or in asample stage before the sample is analyzed, or after said sample hasbeen analyzed, by the measuring tip; and b. an examination unit that isembodied to examine the measuring tip with the aid of the at least onetest structure deposited and/or etched on the sample and/or the samplestage with the aid of a particle beam.
 19. The apparatus of claim 18,further comprising a displacement unit that is embodied to bridge adistance between a point of incidence of a particle beam of thegeneration unit on the sample and/or the sample stage and an interactionlocation between the sample and/or the sample stage and the measuringtip.
 20. The apparatus of claim 18, embodied to carry out the methodsteps comprising: generating at least one test structure before a sampleis analyzed, or after said sample has been analyzed, by the measuringtip, wherein generating the at least one test structure is carried outon the sample and/or a sample stage, and wherein generating the at leastone test structure comprises a particle beam-induced deposition of thetest structure and/or a particle beam-induced etching of the at leastone test structure; and examining the measuring tip with the aid of theat least one test structure deposited and/or etched on the sample and/orthe sample stage with the aid of the particle beam.
 21. A computerprogram comprising instructions that, when executed by a computer systemof an apparatus, prompt a control device of the apparatus to carry outthe method steps comprising: generating at least one test structurebefore a sample is analyzed, or after said sample has been analyzed, bythe measuring tip, wherein generating the at least one test structure iscarried out on the sample and/or a sample stage, and wherein generatingthe at least one test structure comprises a particle beam-induceddeposition of the test structure and/or a particle beam-induced etchingof the at least one test structure; and examining the measuring tip withthe aid of the at least one test structure deposited and/or etched onthe sample and/or the sample stage with the aid of the particle beam.